The present invention relates generally to lay-in lugs and more particularly to techniques for securing a nut plate of a lay-in lug.
Lay-in lugs are similar to “C” or “J” type lugs, as are known, and are used to secure wires (e.g., electrical cables, wiring, tubing, etc.). Lay-in lugs are often used in electrical and similar applications to electrically connect service and/or feed phase-neutral conductors to electrical metering equipment and/or circuit protection. Lay-in lugs may be used in piping systems, such as electrical conduits and the like, to secure wires transposed vertically in a shaft, such as an electrical conduit riser. That is, lay-in lugs are used to hold (e.g., hang) wires vertically.
FIG. 1 is a front perspective view of an exemplary lay-in lug 100 as is known. Lay-in lug 100 has a lug body 102 comprising a base 104 and two opposed and substantially parallel vertical lug walls 106, 108. Supported between and/or atop lug walls 106 and 108 is a removable nut plate 110, which secures a wire binding screw 112.
In use (e.g., in an installation operation), lay-in lug 100 is secured to a surface (not shown) at its base 104. In vertical installation operations, lay-in lug 100 is secured such that the “open” ends 114 and 116 (e.g., sides of lug body 102 not dominated by a lug wall 106, 108) face substantially up and down, respectively (e.g., toward negative X and positive X, respectively). That is, lug walls 106 and 108 will be generally parallel to the direction of a gravity vector G and a secured wire 118. Nut plate 110, with wire binding screw 112 secured thereto, is removed from between lug walls 106, 108. This provides top down (e.g., positive Z to negative Z) access to the center channel 120 of lug body 102. Wire 118 (e.g., electrical cable, wiring, etc.) is laid in, pulled through, or otherwise transposed in the center channel 120 of lug body 102 between lugs walls 106 and 108, generally along the X axis. Nut plate 110 is returned to placement between and/or on top of lug walls 106, 108 and wire binding screw 112 is torqued (e.g., screwed, driven, etc.) to secure wire 118 between base 104 and wire binding screw 112 in the Z direction. Wire 118 is, of course, further secured laterally (e.g., in the Y direction) by lug walls 106, 108.
FIG. 2 depicts a top-front perspective exploded view of another known lay-in lug 200. Lay-in lug 200 is similar to lay-in lug 100 and has a lug body 202 having a lug base 204 and a pair of generally parallel, opposed lug walls 206 and 208. Lay-in lug 200 also has a nut plate 210 (e.g., a lug cap, top, etc.) attachable to the lug body 202 for capture of a wire 118 (e.g., electrical cable, etc.) with wire binding screw 212. As with lay-in lug 100, lay-in lug 200 has “open” ends 214 and 216 and nut plate 210 may be moved along an axis aligned between open ends 214, 216 (e.g., the X axis). The nut plate 210 of lay-in lug 200 has a pair of generally parallel nut plate ears 218 and 220 and respective nut plate flanges 222 and 224. As shown in FIG. 2, each of the nut plate flanges 222, 224 engages a respective lug body flange 226, 228 of the lug body 202. Such flange arrangements, as well as similar ridged arrangements, are used to secure nut plates (e.g., nut plates 110, 210, etc.) to lug bodies (e.g., lug bodies 102, 202, etc.) in a vertical (e.g., Z) direction.
For simplification of discussion, the XYZ axes of FIGS. 1 and 2, as well as FIGS. 3-6 below, may be assumed to be fixed to the lugs 100, 200, 300. Though lugs 100, 200, 300 may be oriented in other manners in real world applications, the lugs 100, 200, 300 are described as non-rotating within the coordinate system. For example, in the context of the present application, the Z axis always refers to the “up-and-down” direction extending through nut plates 110, 210, 310 and bases 104, 204, 304, irrespective of whether lugs 100, 200, 300 are placed on a “ground” surface, mounted to a wall, or are otherwise differently oriented.
The top-down (e.g., Z axis) access simplifies installation of wire 118 over prior “C” or “J” type lugs, but introduces a moveable and easily lost component—nut plate 110/210 with wire binding screw 112/212 attached. That is, since nut plate 110/210 is slideable and removable with respect to the rest of lug 100/200, nut plate 110/210 may inadvertently slide away from lug walls 106/206, 108/208 in transit and/or in installation. This is especially probable and problematic during the aforementioned electrical conduit riser type installation. Since the open end 116/216 of lug body 102/202 faces downward along the X axis (e.g., towards the ground or bottom and generally in the same direction as gravity vector G), nut plate 110/210 is not secured in lug body 102/202 in the vertical (e.g., up and down, along the X axis, etc.) direction and may slide or otherwise fall out due to the force of gravity exerted on nut plate 110/210 and wire binding screw 112/212.
Efforts have been made to prevent loss of nut plate 110/210 and wire binding screw 112/212. Generally, wire binding screw 112/212 is driven (e.g., screwed) through nut plate 110/210 far enough that wire binding screw 112/212 passes through center channel 120 (similarly in FIG. 2) and is bound in lug base 104/204. Lug Body 102/202 may have to be additionally machined to have a counterbore to allow wire binding screw 112/212 to be driven into base 104/204. With the wire binding screw 112/212 driven to contact or otherwise engage (e.g., be limited by) base 104/204, nut plate 110/210 is bi-directionally secured along the X axis and will not slide out as it is constrained in the Y and Z axes by the lug walls 106/206, 108/208 and in the X axis by the interaction of wire binding screw 112/212 with base 104/204. Wire binding screw 112/212 may also engage inner vertical lug walls 106/206, 108/208 (e.g., as with a counterbore, etc.).
These efforts fall short in that wire binding screw 112/212 must be used to secure nut plate 110/210 in the X axis. This is not useful during the installation operations described above because the wire binding screw 112/212 must be disengaged from the base 104/204 when nut plate 110/210 is removed to lay wire 118. During replacement of the nut plate 110/210, gravitational forces act on the nut plate 110/210 in the X direction and the nut plate 110/210 and the wire binding screw 112/212 may fall before the wire binding screw 112/212 is biased against the wire 118 and nut plate 110/210 interacts with the lug walls 106/206, 108/208 (e.g., at flanges 218, 220, 222, and 224 and similarly in lug 100).
Therefore, alternative methods and apparatus are required to secure nut plates in lay-in lugs.